Is it necessary to install a downhole safety valve in a subsea ... - NTNU

Recommendations

Info

Is it necessary to install a downhole safety valve in a subsea oil/gas well? Wellhead seal leak Annulus master valve EXL Annulus wing valve ITL/EXL Tubing hange tubing hanger seal leak Tubing hanger seal annulus bore leak Wellhead 13 5/8" casing seal leak A-annulus area Above tubing Wellhead area Master production valve ITL Crossover line/ annulus area Primary barrier Secodary barrier Third barrier Annulus swab valve ITL/EXL Crossover Annulus master valve ITL Production packer leaks Surroundings Crossover valve, ITL Tubing hanger seal production bore leak A- Annulus Crossover line EXL Production tubing ITL M. Valve Reservoir Crossover valve, EXL Figure 5-4 Barrier diagram for an oil/gas producing well without DHSV Diploma thesis, NTNU 2002 Production swab valve, ITL/EXL Production master valve, ITL Production wing valve, ITL/EXL Above tubing Production master valve, EXL 24
Is it necessary to install a downhole safety valve in a subsea oil/gas well? 5.3 Fault Tree Analysis The construction of the fault trees is based on the theory given in [8]. Fault tree analysis is a deductive technique that focuses on a particular unwanted system event and provides a method for determining causes for that event. A risk analysis often includes the fault tree analysis technique for evaluation of the individual component failure modes and their impact on the system reliability. The fault tree is constructed with the use of different logic gates and displays the interrelationships between a potential critical event in a system and the reasons for this event. The main logic elements are the ‘TOP’-event, the ‘AND’ and ‘OR’ gates, and the basic events. The combination of the basic events and the system structure determines whether or not the ‘TOP’-event will occur. The fault tree provides a static picture of the combinations of failures and events that may cause a ‘TOP’-event to occur. Fault tree analysis, as barrier diagrams, is thus not a suitable technique for analysing dynamic systems. 5.3.1 Case example In the case example the ‘TOP’-event is “leakage to the surroundings”. The ‘TOP’-event occurs either if there is a “leakage to the surroundings from the x-mas tree” or “leakage to the surroundings from the wellhead”. A more concise definition of the ‘TOP’ event is: “Sustainable leakage to the surroundings through either the x-mas tree or the wellhead during normal shut-in conditions.” This ‘TOP' event covers situations where the barrier combination in one or more cut sets have failed. The different components of the production well presented in subsection 5.1.2, are represent basic events in the fault trees. The barrier diagrams, of subsection 5.2.1, provide the basis for the fault tree construction. In order to simplify the construction of the fault tree, external stress and common cause failures are not included. The fault trees constructed for the oil/gas production well with and without a DHSV are presented in appendix C. The CARA-fault tree program is used in the construction. Diploma thesis, NTNU 2002 25
Page 1 and 2: Is it necessary to install a downho
Page 33: Is it necessary to install a downho
Page 69 and 70: APPENDIX A A1 Subsea production sys
Page 71 and 72: A1.3 Well completion A1.3.1 Tubing
Page 73 and 74: A1.5.2 Guidelineless system Several
Page 75 and 76: Appendix B In this appendix a figur
Page 77 and 78: Appendix C Fault trees constructed
Page 79 and 80: Production Wing valve ITL WV Produc
Page 81 and 82: Component: Production Packer Failur
Page 83 and 84: Reliability data dossier Component:
Page 85 and 86:
Component: Production wing valve Fa
Page 87 and 88:
Component: Crossover line Failure r
Page 89:
Appendix F The guide-words used in
show all

Is it necessary to install a downhole safety valve in a subsea ... - NTNU

Create successful ePaper yourself

Delete template?

Save as template?